Elemental mercury is formed in aqueous solution by the chemical reduction of mercuric ion in the presence of humic acid. The reduction proceeds via first order kinetics (rate constant, 0.009 hour-(1)) and is depndent on pH. The reaction mechanism involves interaction of the ionic metal species with the free radical electrons of the humic acid.

. Can. J. Chem. 56,2237Chem. 56, (1978.The assignments of the hydroxyl, hydroperoxyl, and alkylperoxyl radical spin adducts of a-phenyl N-tert-butyl nitrone (PBN) are discussed. Results of new experiments designed to test the assignments of the first two are described. It is concluded that the hydroxy adduct assignment is correct. The relationship between upH and a N is This equation gives a good fit for the seven pairs of constants reported for the hydroxy adduct.

Sir: The writer is grateful to Dr. Alan D. Pethybridge (University of Reading, U.K.) for calling attention to errors in the text of the above paper.1 In the original manuscript, the symbol c, = cy was used for ionic concentration; the subscript i was inadvertently omitted in the text. In accordance with the definition of by (1.8), the factor y1/2 should be inserted after c1/2 in the following places:

Azidyl, cyanatyl, and cyanyl radicals and chlorine atoms have been detected by spin trapping using α-phenyl N-tert-butyl nitrone (PBN) in the monoelectronic electrooxidations of azide, cyanate, cyanide, and chloride. Azidyl and cyanatyl radicals were also detected with PBN in the persulfate oxidations of azide and cyanate. Azidyl radicals could be detected in the reaction of azide with hydroxyl radicals in the presence of PBN.

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